In the fabrication of integrated circuitry, electrically conductive contacts are commonly made to electrically interconnect devices received at different elevations within a substrate. One technique for doing so forms a contact opening within insulative material to an underlying area within the substrate. The contact opening is then typically filled with an electrically conductive material which interconnects with or forms a part of an overlying device.
Exemplary prior art problems which motivated this invention are described with reference to FIG. 1. FIG. 1 depicts a semiconductor substrate 10 comprised of a bulk monocrystalline silicon substrate 12 having various layers formed thereover. The particular problem described is with respect to making a contact opening to a node location 18 within substrate 12, although the problem which motivated the invention manifests regardless of the underlying node location/area to which a conductive contact is being formed. For example, the conductive contact might be formed to any node location, whether comprised of semiconductive material, conductively doped semiconductive material, elemental metals, metal alloys, metal compounds, whether the node location is conductive or semiconductive at the time of the fabrication, etc. FIG. 1 depicts an updoped SiO2 layer 14 received over monocrystalline silicon material 12. A doped SiO2 layer 16, for example borophosphosilicate glass (BPSG), is formed over layer 14. A conductively doped diffusion region 18 has been fabricated within monocrystalline silicon material 12 and comprises a node location to which the conductive contact is being formed.
A contact opening 20 has been anisotropically etched through layers 16 and 14 to diffusion region 18. Ideally, such opening would have straight vertical sidewalls in the substrate orientation depicted in FIG. 1. However more typically a profile as depicted by solid lines 20 in FIG. 1 is a common result, whereby the opening widens slightly at the beginning of the etch and narrows towards the end of the etch. A maximum open width “A” is shown at the outermost portion of opening 20 at the conclusion of the etch.
A conductive material (not shown), for example comprising elemental tungsten, is deposited over layer 16 effective to fill opening 20. At this point in the process, such is typically then polished back, for example by chemical mechanical polishing, at least to the outer surface of layer 16, and typically slightly therebeyond to ensure the complete removal of all conductive material above layer 16.
However prior to deposition of the conductive material, the contact opening which was previously formed is typically subjected to one or more cleaning steps primarily for the purpose of providing a clean, exposed surface on the depicted node location 18. The anisotropic etching depicted to produce FIG. 1, as well as exposure of the substrate to subsequent atmospheres, can leave or form a thin oxide layer over diffusion region 18. This is typically cleared by a suitable liquid etching chemistry prior to deposition of the conductive material to assure electrical contact of the same with diffusion region 18. For example, all of layer 14 might not be cleared by the anisotropic etching depicted to form contact opening 20, and/or a native oxide might form over diffusion region 18. By way of example only, any such oxide can be cleared with a suitable etching chemistry, for example dipping or spraying the substrate with an HF chemistry.
Unfortunately, the typical wet oxide cleans have a tendency to widen the contact opening, for example as depicted by the outline of dashed lines 20a. Further, such widening is not as precisely controllable as one would prefer. Accordingly, the outermost portion of the contact opening can be widened from initial dimension “A” to a subsequent wider dimension “B”. Further because of the typical contact opening profile depicted in FIG. 1, a typical over-polish of the subsequently deposited conductive material will also go into layer 16 to some degree which is also not precisely controllable. As the initially etched contact opening profile widens to some degree in going from the outermost surface of layer 16 to elevationally inward at least initially, this further contributes to uncontrolled widening of contact opening 20/20a. 
Integrated circuitry fabrication continues to strive to make ever denser circuitry devices and components such that the conductive contacts are continually placed closer and closer together. Accordingly, it is desirable to precisely control the maximum width of the conductive contacts to facilitate controlling the critical dimension between immediately adjacent contacts. The lack of contact width control due to contact widening from the clean etching chemistries and over-polishing of material 16 to form the contacts is counter to the dimension control of individual contacts and accordingly to control of the critical dimension between adjacent contacts.
While the invention was motivated in addressing and improving on the above-described issues, it is in no way so limited. Rather, the invention is limited only by the accompanying claims as literally worded, without limiting reference to the drawings or specification or problem(s) as just described, and in accordance with the doctrine of equivalents.